1. Field of the Invention
This invention relates to a transfer member, a process for producing the transfer member, and an image-forming apparatus having the transfer member.
2. Related Background Art
Image-forming apparatus making use of an intermediate transfer member which is one of transfer members are effective as full-color image-forming apparatus or multi-color image-forming apparatus in which a plurality of component color images corresponding to full-color image information or multi-color image information are sequentially superimposingly transferred to output image-formed articles on which full-color images or multi-color images have synthetically been reproduced, or as image-forming apparatus made to have the function of full-color image formation or the function of multi-color image formation.
An example of an image forming apparatus employing an intermediate transfer belt which is a belt-form transfer member is schematically shown in FIG. 1.
The apparatus shown in FIG. 1 is a full-color image-forming apparatus (copying machine or laser beam printer) utilizing an electrophotographic process. A medium-resistance elastic material is used in an intermediate transfer belt 20.
Reference numeral 1 denotes a drum-shaped electrophotographic photosensitive member repeatedly used as a first image bearing member (latent-image-bearing member), which is rotatingly driven at a prescribed peripheral speed (process speed) in the direction of an arrow.
The photosensitive drum 1 is, in the course of its rotation, uniformly charged to prescribed polarity and potential by means of a primary charging assembly 2, and then imagewise exposed to light 3 by an exposure means (e.g., a color-original image color-separating/image-forming optical system, or a scanning exposure system comprising a laser scanner that outputs laser beams modulated in accordance with time-sequential electrical digital pixel signals of image information). Thus, an electrostatic latent image is formed which corresponds to a first color component image (e.g., a yellow color component image) of the intended color image.
Next, the electrostatic latent image formed is developed with a first-color yellow toner Y by means of a first developing assembly (yellow color developing assembly 41). At this stage, second to fourth developing assemblies (magenta color developing assembly 42, cyan color developing assembly 43 and black color developing assembly 44) each stand unoperated and do not act on the electrophotographic photosensitive member 1, and hence the first-color yellow toner image is not affected by the second to fourth developing assemblies.
The intermediate transfer belt 20 is clockwise rotatingly driven at the same peripheral speed as the electrophotographic photosensitive member 1.
The first-color yellow toner image formed and held on the electrophotographic photosensitive member 1 passes a nip formed between the electrophotographic photosensitive member 1 and the intermediate transfer belt 20, in the course of which it is successively intermediately transferred to the periphery of the intermediate transfer belt 20 (primary transfer) by the aid of an electric field formed by a primary transfer bias applied to the intermediate transfer belt 20 through a primary transfer roller 62.
The electrophotographic photosensitive member 1 surface from which the first-color yellow toner image has been transferred to the intermediate transfer belt 20, is cleaned by a cleaning assembly 13.
Subsequently, the second-color magenta toner image, the third-color magenta toner image and the fourth-color black toner image are sequentially similarly transferred superimposingly onto the intermediate transfer belt 20. Thus, synthesized color toner images corresponding to the intended full-color image is formed.
Reference numeral 63 denotes a secondary transfer roller, which is provided in such a way that it is axially supported in parallel to a secondary transfer opposing roller 64 and stands separable from the bottom surface of the intermediate transfer belt 20.
The primary transfer bias for sequentially superimposingly transferring the first- to fourth-color toner images from the electrophotographic photosensitive member 1 to the intermediate transfer belt 20 is applied from a bias source 29 in a polarity (+) reverse to that of each toner. The voltage thus applied is, e.g., in the range of from +100 V to +2 kV.
In the step of primary transfer of the first- to third-color toner images from the electrophotographic photosensitive member 1 to the intermediate transfer belt 20, the secondary transfer roller 63 may also be set separable from the intermediate transfer belt 20.
The synthesized color toner images transferred to the intermediate transfer belt 20 are transferred to a second image bearing member, transfer medium P, in the following way: The secondary transfer roller 63 is brought into contact with the intermediate transfer belt 20 and simultaneously the transfer medium P is fed at a prescribed timing from a paper feed roller 11 through a transfer medium guide 10 until it reaches a contact nip formed between the intermediate transfer belt 20 and the secondary transfer roller 63, where a secondary transfer bias is applied to the secondary transfer roller 63 from a power source 28. On account of this secondary transfer bias, the synthesized color toner images are transferred from the intermediate transfer belt 20 to the second image bearing member transfer medium P (secondary transfer). The transfer medium P to which the toner images have been transferred are guided into a fixing assembly 15 and are heat-fixed there.
After the toner images have been transferred to the transfer medium P, a charging member 7 for cleaning is brought into contact with the intermediate transfer belt 20, and a bias with a polarity reverse to that of the electrophotographic photosensitive member 1 is applied, whereupon electric charges with a polarity reverse to that of the electrophotographic photosensitive member 1 are imparted to toners not transferred to the transfer medium P and remaining on the intermediate transfer belt 20 (i.e., transfer residual toners). Reference numeral 26 denotes a bias power source.
The transfer residual toners are electrostatically transferred to the electrophotographic photosensitive member 1 at the nip between the electrophotographic photosensitive member 1 and the intermediate transfer belt 20 and the vicinity thereof, thus they are removed from the intermediate transfer belt 20.
Compared with a prior art transfer unit in which toner images are transferred from a first image bearing member to a second image bearing member (transfer medium) fastened or attracted onto a transfer drum as disclosed in, e.g., Japanese Patent Application Laid-open No. 63-301960, full-color electrophotographic apparatus having an image-forming apparatus making use of the intermediate transfer member described above have an advantage that a variety of second image bearing member transfer mediums can be selected without regard to their width and length, including thin paper (40 g/m2 paper) and up to thick paper (200 g/m2 paper) such as envelopes, post cards and labels. This is because any processing or control (e.g., the transfer material is held with a gripper, attracted, and made to have a curvature) is not required for the second image bearing member transfer material.
Because of such advantages, full-color copying machines and full-color printers making use of intermediate transfer belts have already begun to be available in the market.
An example of an image-forming apparatus employing a belt-form transfer-transport belt as a transfer-transport (image-transferring and paper-transporting) member which is one of transfer members is schematically shown below in FIG. 2.
The image forming apparatus shown in FIG. 2 is, as one type of a full-color image-forming apparatus of color-separated image superimposing transfer system, an apparatus in which different color toner images are respectively formed on a plurality of photosensitive members, and the toner images on the respective photosensitive members are transferred, under registration, to a single sheet of transfer medium transported in sequential contact with the respective photosensitive members, thus a full-color image is obtained.
The image forming apparatus shown in FIG. 2 comprises, as electrophotographic processing means, four image forming sections I, II, III and IV arranged side by side at the upper part of an apparatus main body 320. The image forming sections I, II, III and IV are respectively constituted of electrophotographic photosensitive members 301Y, 301M, 301C and 301BK as image bearing members, primary charging rollers 302Y, 302M, 302C and 302BK as primary charging assemblies, exposure units 303Y, 303M, 303C and 303BK, developing assemblies 304Y, 304M, 304C and 304BK, and cleaners 305Y, 305M, 305C and 305BK. The developing assemblies 304Y, 304M, 304C and 304BK hold a yellow (Y) toner, a magenta (M) toner, a cyan (C) toner and a black (BK) toner, respectively.
A transfer assembly 310 is also provided at the lower part of the image forming sections I to IV. The transfer assembly 310 is constituted of an endless transfer-transport belt 314 provided stretchingly across a drive roller 311, a follower roller 312 and a tension roller 313, and transfer charging assemblies 315Y, 315M, 315C and 315BK provided opposingly to the electrophotographic photosensitive members 301Y, 301M, 301C and 301BK of the image forming sections I, II, III and IV, respectively.
Meanwhile, at the bottom of the apparatus main body 320, a cassette 306 is provided in which a multiple sheet of transfer mediums (recording paper) P can superposingly be held as recording mediums. The transfer mediums P held in the cassette 306 are sheet by sheet sent out by a paper feed roller 307, and are transported to a registration roller 309 through a transport guide 308.
A separation charging assembly 316 and a fixing assembly 317 are provided on the downstream side in the transport direction of the transfer medium P in the apparatus main body 320, and a paper output tray 318 is installed on the outside of the apparatus main body 320.
In the image forming sections I, II, III and IV, the electrophotographic photosensitive members 301Y, 301M, 301C and 301BK are rotatingly driven at a prescribed speed in the direction of an arrow shown in the drawing, and these are uniformly electrostatically charged by means of the primary charging rollers 302Y, 302M, 302C and 302BK, respectively. The electrophotographic photosensitive members 301Y, 301M, 301C and 301BK thus charged are exposed to light by means of the exposure units 303Y, 303M, 303C and 303BK, respectively, in accordance with image information, whereupon electrostatic latent images are formed on the respective electrophotographic photosensitive members 301Y, 301M, 301C and 301BK. The electrostatic latent images are developed by means of the developing assemblies 304Y, 304M, 304C and 304BK to become visible images as a yellow toner image, a magenta toner image, a cyan toner image and a black toner image, respectively.
Meanwhile, the transfer medium P transported from the cassette 306 to the registration roller 309 through the transport guide 308 is sent out to the transfer assembly 310 by the registration roller 309 under timing, and is then attracted to the transfer-transport belt 314 and passed through the respective image forming sections I, II, III and IV together with the belt, in the course of which the yellow toner image, the magenta toner image, the cyan toner image and the black toner image are superimposingly transferred to the transfer medium P by the operation of the transfer charging assemblies 315Y, 315M, 315C and 315BK, respectively.
Then, the transfer medium P to which the color toner images have been transferred as described above is destaticized by the separation charging assembly 316 to become separated from the transfer-transport belt 314, and thereafter transported to the fixing assembly 317, where the color toner images are heat-fixed to form a full-color image. The transfer medium P with the full-color image is finally put out of the apparatus main body 320, and laid on the paper output tray 318.
The full-color image-forming apparatus employing the transfer-transport belt described above has an advantage that images can be reproduced in a short time because the respective color images are superimposingly transferred while the transfer medium is sequentially transported to the respective image-forming sections.
Because of such an advantage, full-color copying machines and full-color printers making use of transfer-transport belts have already begun to be available in the market.
However, have these full-color image-forming apparatus employing such an intermediate transfer belt or transfer-transport belt functioned as apparatus which well make the most of the above advantages and afforded true expectations, and also given satisfaction, to users? The answer is xe2x80x9cNoxe2x80x9d. In providing the full-color image-forming apparatus employing such an intermediate transfer belt or transfer-transport belt, problems to be overcome as stated below are still unsettled.
In the preparation of intermediate transfer belt or transfer-transport belt, a polyether-ester amide is mixed in a thermoplastic resin in some cases so as to endow the belt with an appropriate electrical resistivity. It, however, has been found that, as seen from Japanese Patent Publication No. 8-7505, when it is mixed in a proportion of 20% by weight or less, a fine unevenness in conductivity due to the island-in-sea structure which is a mechanism by which the polyether-ester amide exhibits conductivity may occur to cause fine image unevenness (the fine image unevenness herein referred to is meant to be a condition in which any unevenness is not recognizable on high-density line images such as character prints but minute streaky unevenness is recognizable on images having an intermediate tone and large area such as halftone images). More specifically, if the polyether-ester amide is less than 20% by weight, dispersion of the polyether-ester amide (islands) in the thermoplastic resin (sea) may stand coarse, so that the spaces may be produced so greatly that portions having a conductivity (i.e., portions comprised only of the polyether-ester amide) and portions having no conductivity (i.e., portions comprised only of the thermoplastic resin) appear on images in some cases. This has often made it difficult to obtain products which are satisfactory on images.
An object of the present invention is to provide a high-quality intermediate transfer member and transfer member which may cause no faulty images when toner images are transferred from the first image-bearing member to the intermediate transfer member and transferred from the intermediate transfer member to the second image-bearing member, or when transferred from the first image-bearing member to the second image-bearing member.
To achieve the above object, the present invention provides a transfer member having at least a resin layer, wherein the resin layer contains a thermoplastic resin and a polyether-ester amide, and the thermoplastic resin and the polyether-ester amide are in a weight ratio of from 79:21 to 60:40.
The present invention also provides a process for producing a belt-form transfer member, wherein a material containing a thermoplastic resin and a polyether-ester amide, the thermoplastic resin and the polyether-ester amide being in a weight ratio of from 79:21 to 60:40, is extruded from a circular die to form a tube, and then the tube is cut to obtain a seamless belt.
The present invention still also provides an image-forming apparatus having the above transfer member.